Index: Python/ast.c
===================================================================
--- Python/ast.c	(revision 46757)
+++ Python/ast.c	(working copy)
@@ -1430,10 +1430,18 @@
                          LINENO(n), n->n_col_offset, c->c_arena);
     }
     else {
+        int nch_n;
         REQ(CHILD(n, 0), LSQB);
-        REQ(CHILD(n, 2), RSQB);
-        n = CHILD(n, 1);
-        if (NCH(n) == 1) {
+        if (NCH(n) == 3) {
+                REQ(CHILD(n, 2), RSQB);
+                n = CHILD(n, 1);
+                nch_n = NCH(n);
+        }
+        else {
+                REQ(CHILD(n, 1), RSQB);
+                nch_n = 0;
+        }
+        if (nch_n == 1) {
             slice_ty slc = ast_for_slice(c, CHILD(n, 0));
             if (!slc)
                 return NULL;
@@ -1450,10 +1458,10 @@
             expr_ty e;
             bool simple = true;
             asdl_seq *slices, *elts;
-            slices = asdl_seq_new((NCH(n) + 1) / 2, c->c_arena);
+            slices = asdl_seq_new((nch_n + 1) / 2, c->c_arena);
             if (!slices)
                 return NULL;
-            for (j = 0; j < NCH(n); j += 2) {
+            for (j = 0; j < nch_n; j += 2) {
                 slc = ast_for_slice(c, CHILD(n, j));
                 if (!slc)
                     return NULL;
Index: Grammar/Grammar
===================================================================
--- Grammar/Grammar	(revision 46757)
+++ Grammar/Grammar	(working copy)
@@ -119,7 +119,7 @@
 listmaker: test ( list_for | (',' test)* [','] )
 testlist_gexp: test ( gen_for | (',' test)* [','] )
 lambdef: 'lambda' [varargslist] ':' test
-trailer: '(' [arglist] ')' | '[' subscriptlist ']' | '.' NAME
+trailer: '(' [arglist] ')' | '[' [subscriptlist] ']' | '.' NAME
 subscriptlist: subscript (',' subscript)* [',']
 subscript: '.' '.' '.' | test | [test] ':' [test] [sliceop]
 sliceop: ':' [test]
Index: Modules/parsermodule.c
===================================================================
--- Modules/parsermodule.c	(revision 46757)
+++ Modules/parsermodule.c	(working copy)
@@ -2713,7 +2713,7 @@
 
 /*  trailer:
  *
- *  '(' [arglist] ')' | '[' subscriptlist ']' | '.' NAME
+ *  '(' [arglist] ')' | '[' [subscriptlist] ']' | '.' NAME
  */
 static int
 validate_trailer(node *tree)
@@ -2729,9 +2729,9 @@
                 res = validate_arglist(CHILD(tree, 1));
             break;
           case LSQB:
-            res = (validate_numnodes(tree, 3, "trailer")
-                   && validate_subscriptlist(CHILD(tree, 1))
-                   && validate_ntype(CHILD(tree, 2), RSQB));
+            res = validate_ntype(CHILD(tree, nch - 1), RSQB);
+            if (res && (nch == 3))
+                res = validate_subscriptlist(CHILD(tree, 1));
             break;
           case DOT:
             res = (validate_numnodes(tree, 2, "trailer")